Cap for a rail insulator



FIG. 1 is a perspective view of a cap for a rail insulator showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a right side elevational view thereof, with a left side elevational view being a mirror image thereof; and,

FIG. 5 is a front elevational view thereof, with a rear elevational view being a mirror image thereof.

In the drawings, the broken lines depict unclaimed subject matter only and form no part of the claimed design. 

CLAIM The ornamental design for a cap for a rail insulator, as shown and described. 